WO9415157 discloses a water treatment system in which the water to be recycled is fed to a first stage separator in the form of a settling chamber, in which solids particles settle out. Periodically, a fluidising device is operated to discharge these particles to a drain.
The water, from which the solids particles have settled out, overflows to a tank and is then pumped through a liquid/liquid hydrocyclone to carry out a secondary treatment stage which removes contaminants that are lighter than water through the hydrocyclone overflow. The treated water is discharged through the hydrocyclone underflow and pumped to a high level treated water storage tank. The tank may be connected to a dedicated pipe system to distribute the water, by gravity, to WC cisterns or urinals.
In the water treatment system of WO9416157 the water to be treated has to pass through two different stages. As a result, the system is complicated to construct and has numerous parts, making it difficult to manufacture and install, whilst also producing doubtful water quality. This leads to high build and installation costs, making it unsuitable for the average consumer market.
CN101352629 discloses a water treatment device comprising a filter chamber with an internal filter body. Water enters the filter chamber tangentially and circulates around an annulus formed by the chamber and the filter body, allowing heavy large particles to drop out under gravity. A large proportion of water flows radially into the filter body to be filtered by filter media. The filtered water is transferred to a storage tank for later use.
Grey water typically contains contaminants such as soap, shampoo and detergents. Thus, for example, a synthetic grey water designated “Class 1 Basic Grey Water” is defined as follows:
The recipe to formulate 100 liters of “Class 1 Basic Grey Water” is as follows:                97.5 liters of tap water at 30° C.        86 ml shampoo and/or liquid soap.        1 ml sunflower oil.        2.5 liters tertiary treated sewage effluent with >106 cfu/100 ml total coliforms.(Source: Building Services Research and Information Association (BSRIA) Water Reclamation Standard for Laboratory testing of systems using grey water, Technical note TN July 2002, by Reginald Brown and Anu Palmer.)        
The microbiological Water Quality to be achieved by treatment processes for water to be made available for WC flushing is:                Total coliforms<100 cfu/100 ml.        Samples shall be visually clear and free from floating particles and sediment        The Opacity of any reclaimed water shall not exceed 60% when measured at 254 nm.        Dissolved oxygen shall not fall below the lesser of 10% saturation or 1 mg/liter.        Total Chlorine less than 2 ppm or equivalent        
The microbiological Water Quality to be achieved by treatment processes for water to be made available for Drip and trickle irrigation is:                Total coliforms<1000 cfu/100 ml.        Samples shall be visually clear and free from floating particles and sediment        The Opacity of any reclaimed water shall not exceed 60% when measured at 254 nm.        Dissolved oxygen shall not fall below the lesser of 10% saturation or 1 mg/liter.        Total Chlorine less than 0.5 ppm or equivalent        
The microbiological Water Quality to be achieved by treatment processes for water to be made available for vehicle washing is:                Total coliforms<10 cfu/100 ml.        Samples shall be visually clear and free from floating particles and sediment        The Opacity of any reclaimed water shall not exceed 60% when measured at 254 nm.        Dissolved oxygen shall not fall below the lesser of 10% saturation or 1 mg/liter.        Total Chlorine less than 0.5 ppm or equivalent        
The water treatment system described in CN101352629 suffers from the following problems:                1. The liquid soap used in the BSRIA synthetic grey water recipe causes foaming of the water entering the filter body. The media bed is then blinded by the foam, which is a soap and air emulsion, severely restricting the flow through the filter media. As a result, there is excessive water back up in the filter so that a significant volume of incoming water passes to the drain.        2. The foam overflows the central filter chamber with the result that the foamed, untreated water migrates into the treated water in the bottom of the system, leading to contamination of the previously treated water.        3. Incoming water flowrates into the filter body can be relatively high (for example in excess of 0.4 l/s); this flow rate is sufficient to displace filter media within the media support screen.        4. Control of disinfectant dosing levels is inadequate.        5. The system includes a coarse strainer having an inlet strainer basket which is difficult to remove and replace.        6. Drainage of the high level storage tank would not work as envisaged owing to the requirement to have a minimum level of potable water available at all times should treated water not be available. The storage tank also requires separate supply and discharge pipes.        